Seems to me what she is asking for is a god-sanctioned end to a relationship that she is likely NOT very comfortable with. Her ability to deal with a non-believer is shaky at best and, to put the worst spin I can think of on it, she's asking her deity to commit murder so that she no longer has to be confronted with his heresy ... or equally likely, doesn't have to suffer the cognitive dissonance implicit in his presence and lack of belief.

HOLY CRAP! I'm really sorry for anything I say that might offend you...
But yeah she's totally nuts! Are you kidding with this story? She's basically asking god to toy with your life purely out of her own curiosity.
It seems kinda like she's way too religious for her own good.

This is just my interpretation, I know neither of you so I could be way off base here. It sounds to me like she was angry about the argument, and while angry wishing for a way out of the situation. I think she may have felt guilty on some level for her feelings, and in that state of mind prayed for a solution. Telling you about it may have been a combination of guilt regarding the prayer, a means to let you know just how upset she was, and a way of affirming her commitment to you despite these feelings.

Nah, I don't think she's praying for your death; more like she's seeking reinforcement for her decision to marry you. It's the same as "If my beloved is at the bus stop this morning,, that means god wants us to be together..." or "If he/she accepts a chocolate from me that means he/she REALLY loves me...." Totally ridiculous, but that's what I think. We all seek meaning for our decisions and what happens to and around us. It's not about you, it's about your wife's attachment to her beliefs and her need for vindication and coping, should you, by some unforeseen misfortune, not had made it through surgery. Give her a kiss and tell her you love her. It wouldn't hurt to take a few precautions, though.............